Write head control device for ink jet printer utilizing liquid metal and method thereof

ABSTRACT

To maintain a temperature of a liquid metal mass utilized in a write head for an ink jet printer, an improved control device is disclosed which comprises a heating element and a temperature sensor element. In the disclosure, there is provided a write hood device in an ink printer equipment having at least an ink storage chamber inside body of the head, a nozzle for ejecting an ink droplet at one portion of the chamber, an ink channel formed to connect the chamber and an ink cartridge, a pair of electrodes provided at another portion of the chamber and each disposed opposite to each other for charging a liquid metal mass with electricity, a pair of magnetic substances symmetrically disposed to face each other and disposedly arranged at an angle of 90°; with respect to the magnetic substances, wherein said liquid metal mass movably contained at the bottom of the chamber for purging ink to discharge an ink, droplet, said write head comprising; a temperature sensor element for sensing a temperature at a predetermined portion of said write head: and a heating element provided at a predetermined location of said write head, for maintaining the temperature of said liquid metal at a level beyond a prescribed degree by way of directly warming said ink, whereby the temperature of said liquid metal holds a degree of substantially constant level beyond a melting point. As a result, a liquid metal holds the temperature at a substantially constant value during a normal mode of operation, maintaining its phase in liquid state, thereby enhancing the performance of the printer.

CROSS-REFERENCE TO RELATED APPLICATION

This application makes reference to, incorporates the same herein, andclaims all benefits accruing under 35 U.S.C.§119 from an application forPrinting Head Control Apparatus For Ink Jet Printer Utilizing LiquidMetal And Method Thereof earlier filed in the Korean Industrial Propertyon the 25th of Apr. 1995 and assigned Ser. No. 9686/1995 by that Office.

BACKGROUND OF THE INVENTION

The present invention relates to a write head of an ink jet printer, andmore particularly, to a write head control device and process using aliquid metal for ejecting individual ink droplets in liquid state duringan operational mode of the printer.

Typically, an ink storage chamber is provided inside the body of a writehead in a conventional ink printer, and a nozzle ejects individual inkdroplets. The ejection of individual ink droplets from the tip of thenozzle in the write head is subject to the influence of the Lorentzforce equation. Thus the magnitude of a force applied to an ink dropletin the path of magnetic line of force is determined by Fleming'sleft-hand rule. The influence of the electric resistance of the ink isextremely critical for each droplet ejection. I have found that althoughelectric resistance ought to be lower than five Ohms, in actuality thislow a resistance is unattainable.

The use of a either a diaphragm or of liquid metal to eject droplets ofink has also been proposed. The Droplet Deposition Device proposed byStephen Temple et al., in U.S. Pat. No. 4,845,517 suggests a write headfor an ink jet printer employing a liquid metal as a propagativeactuator for applying a force. In this proposal, ink is forced to bedischarged at the tip of nozzle by virtue of a applied kinetic energygenerated by an operation of the Lorentz force equation via liquid metalso that an operation of printing is enabled. Liquid metal is known tohave to hold its temperature at not less than a constant value, e.g.,18° C. so as to remain in a liquid state. As a result, the normaloperation of portraying characters and graphics on a recording medium ishighly dependent upon the temperature of liquid metal since below amelting point temperature the liquid metal assumes the properties ofsolid state, a fact that I have found often hinders the normaloperational mode of an ink jet printer.

SUMMARY OF THE INVENTION

Therefore it is an object of the present invention to provide animproved write head controller for an ink jet printer.

It is another object to provide a write head control device for an inkjet printer utilizing a liquid metal, for controlling a heating elementto hold the temperature of the liquid metal at a constant value above amelting point during an operational mode of a printer.

It is another object to provide a controlling method with an ink jetprinter for controlling the temperature of a liquid metal to maintain aconstant value above a melting point so that a liquid metal remains in aliquid state during an operational mode of a printer.

To achieve these and other objects, there is provided a write head in anink jet printer including a plurality of ink storage chamber inside thebody of a write head; a nozzle for ejecting an ink droplet on the topportion of an ink storage chamber; a plurality of ink channels forflowing an ink supplied from an ink tank; and a pair of electrodes and apair of magnetic substances, symmetrically opposed to each other andeach electrodes arranged to be disposed at an angle of 90 degrees withrespect to magnetic substances, surrounding the periphery of the lowerportion of the ink storage chamber, which head comprises a temperaturesensor for sensing a temperature of a predetermined portion of the writehead and a heating device arranged on the write head so as to maintainthe temperature of a liquid metal at or above a predetermined constantvalue by warming ink.

There is also provided a method for controlling that utilizes a writehead in an ink jet printer the steps of sensing a temperature of apredetermined portion of a write head to detect a temperature of aliquid metal, determining whether the detected temperature is below apreset value, driving a heating device when the detected temperaturefalls under a preset value, and turning off an operation of a heatingdevice when the detected temperature value is beyond a preset value.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention, and many of the attendantadvantages thereof, will be apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings in which likereference numerals and symbols indicate the some or similar components,wherein:

Fig. 1A is a schematic sectional view illustrating a conventionallyconstructed configuration of a write head in an ink jet printeremploying a sole ink storage chamber:

Fig. 1B is an enlarged sectional view of the write head, taken along theline I-I' in FIG. 1A, FIG. 2A is a schematic-sectional view of aconventionally adopted configuration of a write head in an ink jetprinter utilizing a liquid metal;

FIG. 2B is an enlarged sectional view of the write head, taken along theline II-II' in FIG. 2B;

FIG. 3 is a schematic sectional view of one preferred embodiment of awrite head control device constructed according to the principle of thepresent invention;

Fig, 4 is a schematic sectional view of another preferred embodiment ofa write head control device constructed according to the principle ofthe present invention;

FIG. 5 is a schematic circuit diagram of a driving circuit of onepreferred embodiment constructed according to the principle of thepresent invention;

FIG. 6 is a block diagram illustrating a portion of circuitry of an inkjet printer incorporating the driving circuit of FIG. 6; and

FIG. 7 is a flow chart illustrating a sequential order of controllingoperation of a circuit as shown in FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A known principle in an ink printer for portraying characters on arecording medium is based upon ejection of individual ink droplets fromthe nozzle of a write head that is a component part of the printer. Theink drops are usually ejected from the nozzle under the influence of acontroller in an ink printer. Characters and graphic patterns aretypically constructed with a grid-like pattern on the recording mediumby coordinating the ejection of individual droplets and the relativemotion between the recording medium and the write head. The operationalreliability and the quality of the recording are highly dependent on theuniformity of the droplet ejection, i.e., the individual dropletsejected by 2 drive pulse must leave the nozzle of the write head withthe respectively same speed.

Conventionally, the controller in a bubble jet printer provides a writehead with a heating device able to suddenly heat the ink in the regionof an ink channel so as to induce an osmotic action of the ink until anink vapor bubble is formed. Bubbling of ink by the heating device causesejection of ink from a nozzle of a head write in the printer. A heatingdevice of the type describe above serves as a heating element forwarming the ink.

It is known, as evidenced by the Heating Mechanism For Warming The InkIn The Write Head Of An Ink Printer Means in U.S. Pat. No. 5,182,578 toErnst-Goepel et al. to provide a heating device for warming ink in anink channel arranged in a write head of an ink jet printer. The heatingdevice includes a heating element and a temperature sensor arranged on awrite to head carrier as well as a voltage regulator. The heatingelement above disclosed is supplied with a constant load current via aregulating circuit until an adjustable operating temperature is reached.The heating energy for warming the ink is offered via the dissipatedheat of the heating element. In the device of Ernst-Goepel '578, the inkin the type of an ink jet printer is warmed by a heating device equippedwith a temperature sensor element and a voltage regulator with a heatingelement being arranged on the write head carrier.

Due to the frequency of times for warming ink with the heating element,the innate characteristics of an ink become worse. This degradationcauses the expected life span of a write head as well as the heatingelement itself to be short. As a result, a controller constructed with atemperature sensor element and a heating element serving as a heatingdevice for warming the ink and for controlling the temperature of theink, does not guarantee reliable regulation of the temperature.

Referring now to FIGS. 1A and 1B, a detailed explanation for theconventionally employed scheme has an ink storage chamber 12 providedinside body 11 of a write head 10 in a conventional ink jet printer. Anozzle 13 which ejects an individual ink droplets, is provided at thesubstantially centered area of top surface of ink storage chamber. Acouple of ink channels 14 are arranged opposite from each other forsupplying an ink from an outside ink tank (not shown) to the inside ofink storage chamber 12.

A pair of electrodes 16, 17 and a pair of magnetic poles havingrespective N and S polarities as shown are arranged perpendicularly toeach other around the periphery of the lower portion of ink storagechamber 15, so that each of the electrodes is disposed symmetrically andarranged at an angle of ninety degrees relative to each of the magneticpoles.

The behavior of individual ink droplets during ejection from the tip ofnozzle 13 in write head 10 is subject to the influence of the Lorentzforce equation. Thus, the magnitude of a force applied to an ink withinthe path of the magnetic lines of force occurring between a pair ofmagnetic poles 18, 19 is determined by Fleming's left-hand rule. Ink isforced to move commonly perpendicularly to the directions of bothmagnetic flux and current. As a result, each individual ink droplet isdischarged via the ink channel in nozzle 13 by virtue of a combinedforce derived from the magnetic field formed between magnetic poles 18and 19 in combination with an electric field formed between pair ofelectrodes 16 and 17 while supplied with a constant current. Theinfluence of the electric resistance of ink 15 utilized in theconstruction of such write head mechanism is extremely critical forindividual droplet ejection. The electric resistance should be lowerthan 5 Ohms (Ω), a condition that I have found to be unattainable inactuality.

There has been a proposal to employ a diaphragm, for example, such as apiezoelectric material, so that ink 15 is forced indirectly by thediaphragm liquid metal has recently been proposed in lieu of the abovediaphragm. U.S. Pat. No. 4,845,517 to Temple et al, for example,suggests a write head for an ink jet printer employing a liquid metal asa propagative actuator for forcing the ink to travel.

FIGS. 2A and 2B illustrate respective sectional views of a write headwhere liquid metal 20 is utilized in the write head 10 of a ink jetprinter.

In the configuration disclosed in the conventional technique, liquidmetal 20 is supplied to ink storage chamber 12 in a predetermined amountof quantity. Liquid metal can be a compound of indium (In) and gallium(Ga), and would also meet the requirement for electric resistance ofless then five ohms, which is unattainable with the innate property ofan ink. Accordingly, liquid metal serves as an actuator of kineticenergy in lieu of the mass of the ink. Therefore, ink 15 is forced to bedischarged at the tip of nozzle 13 by virtue of an applied kineticenergy generated by an operation of the Lorentz force equation vialiquid metal so that the operation of printing is enabled. Liquid metalserved as above is known to hold the temperature of itself at not lessthan a constant value, e.g., 18° C., so as to remain in a liquid state.I have found that as a result, a normal printing operation of portrayingcharacters and graphics on a recording medium 13 highly dependent on thetemperature of liquid metal since below a melting point temperature, theliquid metal maintains its properties of solid state. Consequently, Ihave noticed that these drawbacks often hinder the normal operationalmode of an ink jet printer.

Referring now to FIG. 3 in conjunction with FIGS. 1B and 2B, there isillustrated one preferred embodiment of a write head control device ofthe present invention. A plurality of ink storage chambers 12 areprovided inside body 11 of a write head 10; the chambers of write head10 are arranged either separately or collectively linked to each otherby respective ink channel 14 in construction. Write head 10 may beconstructed in a configuration having a plurality of linked inkchannels, either with a single ink storage chamber providing massstorage capability or with several isolated ink storage chambers thatwould be available as necessary. A nozzle 13 is provided at a portion ofan ink storage chamber 12, preferably at the top portion thereof,through which an ink droplet is ejected for printing during a printingmode operation. An ink storage chamber is supplied with ink from an inkcartridge 23 via ink channel 14.

At least one ink channel 14 is connected to an ink cartridge 23 forsupplying ink to head 10. A pair of electrodes 16 and 17 are oppositelyprovided in body 11 while a pair of magnetic poles 18 and 19 arearranged at a right angle between each electrode as described in thediscussion of FIGS. 1A and 2B. Also, a mass of liquid metal 20 isprovided at the bottom of chamber 12.

As can be seen in the drawings, a location opposite from nozzle 13 doesnot necessarily refer to a position that is face to face to nozzle 13.Any position will rather do if ejection of ink is performed by actuatingoperation of liquid metal.

According to the present invention, a temperature sensor 21 forindirectly detecting the temperature of the liquid metal mass 20 and aheating element 22 for indirectly heating the liquid metal mass 20 areprovided at, and preferably within, an ink channel 14. Heating element22 heats ink and thus liquid metal mass 20 is indirectly heated by warmink 15 within chamber 12.

According to the principles of the present invention temperature sensor21 and heating device 22 may well be embodied in a write head 10 onevery nozzle 13, or alternately singly or collectively installed toservice groups of blocks as necessary. Heating element 22 heats ink 15and indirectly warms liquid metal 20, and may be positioned any placewithin body 11, thereby enabling direct heating of liquid metal 20. Anylocation may be chosen for heating device 22, for instance, any surfacearea of write head 10, inside ink channel 14, any sidewall of inside inkstorage chamber 12 for containing ink or liquid metal, and inside body11. Additionally, and referring now to FIG. 4, temperature sensor 21Amay be disposed in a location adjacent to liquid metal 20 so as todirectly sense the temperature thereof Thus, any location at which thetemperature of liquid metal 20 be sensed whether directly or indirectly,may be chosen for temperature sensor 21A; for example, within body 11,within the inner sidewalls adjacent to either storage portion of ink orliquid metal in ink storage chamber 12, ink channel 14 and on anysurface portion of head 10.

The electrodes 16 and 17 and magnetic segments 18 and 19 in FIGS. 3 and4 are controlled by a control circuit shown in FIG. 5. The controlcircuit includes a first voltage divider having two fixed resistor R1and R2, and second voltage divider having a fixed resistor R3 and atemperature sensor 21 as an variable resistor. A comparator COM havinginverting and non-inverting input ports and a transistor TR connected toan output of the comparator COM for turning on or off heating element22. Predetermined reference voltage Vref, which is voltage divided byfirst voltage divider, a pair of resistors R1 and R2, connected inseries to a local reference potential such as a ground potential, isapplied to a non-inverting terminal (-) of comparator COM. A potentialVa at a varying voltage level is generated by second voltage divider, atthe junction of resistor R3 and temperature sensor 21, is applied to aninverting terminal (+) of comparator COM. Temperature sensor 21, 21A iscoupled between the non-inverting terminal (+) of comparator COM and thelocal reference potential.

Output terminal of comparator COM is connected to the base electrode oftransistor TR whose emitter electrode is coupled to the local referencepotential and collector electrode is connected to power source +V viaheating element 22. Preferably, temperature sensor 21 is a type of anegative temperature coefficient device and has an internal resistancewhich is adapted to be correspondingly increased as the detectedtemperature is higher than a pre-established temperature which ispreferably in a range extending from about 18° C. to about 23° C.

When the sensor 21 detects a temperature lower than about 18° C. whichis a melting point of the liquid metal, the voltage Va of the secondvoltage divider becomes higher than the reference voltage (Vref) becauseof the increased resistance of the sensor 21. Thus the voltage (Va) issupplied to comparator COM and then comparator COM outputs a high levelsignal to transistor TR to the thereby turn on the heating element 22.

When the temperature detected by sensor 21 is higher than thepre-established temperature, the internal resistance of the sensor 21 islowered and the voltage (Va) of the second voltage divider is lower thanthe reference voltage (Vref) of the first voltage divider, thencomparator COM outputs a low level signal to transistor TR to therebyturn off the heating element 22. Accordingly, the liquid metal can bemaintained in a liquid phase. Here, a predetermined temperature ispreferably in the range of about 0°-5° C. higher than a melting point.As a result, if transistor TR is turned on (i.e., if the principalelectrically conducting channel between the collector and emitterelectrodes is biased at its base control electrode into an electricallyconducting state), then heating element 22 dissipates heats, and thetemperature of liquid metal 20 becomes in turn higher as the temperatureof the ink gets higher.

When the temperature of liquid metal 20 exceeds a predetermined value,then a potential Va becomes lower following the decreased internalresistance of temperature sensor 21, thereby enabling comparator COM togenerate a signal of low level, which in turn cuts off the principalelectrical conduction path in transistor TR between its collector andemitter electrodes. At this moment, heating element 22 cease a heatdissipation. With the above operation described, the temperature ofliquid metal 20 is maintained at a constant level.

FIGS. 6 is a block diagram of a circuit for controlling the heating ofthe mass liquid metal by a sequential operation of software stored in amicroprocessor of a printer. The circuit as shown in FIG. 6 incorporatestemperature sensor 21 for sensing the temperature of ink 15, converter21B for converting an amount of varying resistance of temperature sensor21 into a voltage of constant level, controller 30 for controllingoverall operation of the circuitry in a printer, a memory device 31, forsupplying a prestored data to controller, which device availableinternally or externally by way of a circuit configuration design,driving circuit 22B for driving heating element 22, and heating element22.

Referring to FIG. 7, a flow chart demonstrating a sequential order ofoperation of the circuit of FIG. 6 is illustrated. Firstly, apredetermined program is stored in memory device 31. When the circuit isenergized then the program is read to be executed in controller 30.Temperature sensor 21 senses a temperature on a scale of temperatures,and applies the value of the temperature sensed to convener 21B. Asignal converted in converter 21B on the basis the value of thetemperature sensed is fed to controller 30. (Step S1). Controllerdetermines whether the input signal applied from converter 21Bindicative of the temperature of liquid metal 20, is lower than apredetermined temperature which is preset at a relevant addresses inmemory in step S2.

When it is determined that the input signal represents a degree oftemperature below a preset value, then controller 30 outputs a signal todriving circuit 22B so as to initiate a heat dissipation operation ofheating element 22 in Step S3.

In Step S2 however, if the input signal is determined to indicate avalue higher than a preset reference value, then controller 30 outputsno signal and heating element 22 ceases heat dissipation in Step S4.

Sequential operations performed as above enable liquid metal to hold itstemperature at a constant value, without loss that would drop thetemperature of liquid metal twenty below the critical melting pointtemperature.

As disclosed above, the instant invention embodied in various types ofpreferred embodiments holds the temperature of liquid metal at or abovethe melting point temperature of the composition of liquid phase metalutilized, thereby enabling an operational temperature of a write head tobe properly maintained, thus enhancing overall performance of an ink jetprinter.

While there have been illustrated and described what is to be consideredthe preferred embodiment of the present invention, It will be understoodby those skilled in the art that various changes and modifications maybe made, and equivalents may be substituted for elements thereof withoutdeparting from the true scope of the present invention. In addition,many modifications may be made to adapt a particular situation to theteaching of the present Invention without departing from the scopethereof. Therefore, it is understood that the present invention is notlimited to the particular embodiments disclosed as the beat modecontemplated for carrying out the present invention, but embodimentsfalling within the scope of the appended claims.

What is claimed is:
 1. A write head device for an ink printer using anink cartridge, comprising:an ink storage chamber; nozzle for ejecting anink droplet disposed at one portion of said chamber; an ink channelformed to connect said chamber and the ink cartridge; a pair ofelectrodes provided at another portion of the chamber dispose oppositeto each other for charging a mass of liquid metal within said chamberwith electricity; a pair of magnetic poles symmetrically disposed toface each other on opposite sides of said chamber in an orthogonalarrangement with said pair of electrodes, said liquid metal mass beingmovably contained at a bottom of said chamber for purging ink todischarge in droplets through said nozzle; a temperature sensor elementfor sensing a temperature at a predetermined location of said writehead; and a heating element provided at a another location of said writehead, for operatively responding to signals provided by said temperaturesensor representative of said temperature at said predetermined locationby maintaining the temperature of said liquid metal at a level beyond aprescribed degree by directly warming said ink, and maintaining saidliquid metal at a temperature exhibiting a substantially constant levelabove a melting point of said liquid metal.
 2. The write head device ofclaim 1, further comprised of a unit of several blocks of individualnozzles, with at least a pair of said temperature sensor element andheating element being employed in said write head commonly shared bysaid unit of several blocks.
 3. The write head device in an ink printerequipment as claimed in claim 1, wherein said temperature sensor elementis incorporated any location of said write head.
 4. The write headdevice in an ink printer equipment as claimed in claim 1, furthercomprised of said temperature sensor element being provided at alocation substantially adjacent to an ink storage portion of saidchamber.
 5. The write head device in an ink printer equipment as claimedin claim 1, further comprised of said temperature sensor element beingprovided at a location substantially adjacent to an liquid metal storageportion of said chamber.
 6. The write head device in an ink printerequipment as claimed in claim 1, further comprised of said temperaturesensor element being provided at inner surface of said ink channel. 7.The write head device in an ink printer equipment as claimed in claim 1,further comprised of said heating element being positioned at aprescribed location on a surface area of said write head.
 8. The writehead device in an ink printer equipment art claimed in claim 1, furthercomprised of said heating element being provided at a prescribedlocation of said chamber.
 9. The write head device in an ink printerequipment as claimed in claim 1, further comprised of said heatingelement being provided at a location substantially adjacent to an inkstorage portion of said chamber.
 10. The write head device in an inkprinter equipment as claimed in claim 1, further comprised of saidheating element being provided at a location substantially adjacent to aliquid metal storage portion of said chamber.
 11. The write head devicein an ink printer equipment as claimed in claim 1, further comprised ofsaid heating element being provided at an inner surface of said inkchannel.
 12. The write head device for an ink printer of claim 1, withsaid temperature sensor element and heating elements further comprisinga circuit comprised of:a first pair of voltage dividing resistorsconnected in series, for supplying a reference voltage at a constantlevel from a junction node; a second pair of voltage dividing resistorscomprising a resistor and said temperature sensor element, connected inseries for supplying varying voltage; a comparator comparing saidreference voltage with said varying voltage to output a signal at anoutput terminal of said comparator; and a transistor having a controlelectrode coupled to said output terminal of said comparator, an emitterelectrode coupled to a reference potential and a collector electrodecoupled to a power source via said heating element.
 13. A method forcontrolling a write head in an ink printer equipment utilizing a liquidmetal mass, said method comprising the steps of:sensing a temperature ata predetermined location on said write head to detect the temperature ofsaid liquid metal; determining whether said detected temperature fallsbelow a preset value; driving a heating element when the detectedtemperature is below said preset value; and turning off an operation ofsaid heating element when the detected temperature is beyond saidpreset.